Wireless power reception method of a wireless power receiver in which first demanded power of the wireless power receiver is adjusted within a first available power of the wireless power tansmitter

ABSTRACT

A method for transmitting wireless power from a wireless power transmitter, the method can include performing a negotiation process with a wireless power receiver for generating a negotiated power transmission condition, the negotiation process including receiving a request signal from the wireless power receiver to retrieve a capability of the wireless power transmitter, the capability including an available amount of power of the wireless power transmitter, transmitting the available amount of power to the wireless power receiver, in response to the request signal, to allow the wireless power receiver to determine a demanded amount of power based on the available amount of power of the wireless power transmitter, and subsequently, receiving the demanded amount of power as the negotiated power transmission condition from the wireless power receiver; and transmitting wireless power to the wireless power receiver based on the negotiated power transmission condition when the demanded amount of power is allowable by the wireless power transmitter based on the capability of the wireless power transmitter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/071,428, filed on Mar. 16, 2016, which is a continuation of U.S.patent application Ser. No. 14/616,367, filed on Feb. 6, 2015 (now U.S.Pat. No. 9,728,980, Issued on Aug. 8, 2017), which is a divisional ofU.S. patent application Ser. No. 13/673,163, filed on Nov. 9, 2012 (nowU.S. Pat. No. 9,197,070, Issued on Nov. 24, 2015), which claims thebenefit of Patent Application No. 10-2011-0117233, filed in Korea onNov. 10, 2011, all of which are hereby expressly incorporated byreference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The embodiment relates to a wireless power transmitter, a wireless powerreceiver, a wireless power transmission method and a wireless powerreception method. In more particular, the embodiment relates to awireless power transmission for actively transmitting power according topower transmission state between a wireless power transmitter and awireless power receiver.

Discussion of the Related Art

A wireless power transmission or a wireless energy transfer refers to atechnology for wirelessly transferring electric energy to desireddevices. In the 1800's, an electric motor or a transformer employing theprinciple of electromagnetic induction has been extensively used andthen a method for transmitting electric energy by irradiatingelectromagnetic waves, such as radio waves or lasers, has beensuggested. Actually, electric toothbrushes or electric razors, which arefrequently used in daily life, are charged based on the principle ofelectromagnetic induction. Until now, the long-distance transmissionusing the magnetic induction, the resonance and the short-wavelengthradio frequency has been used as the wireless energy transfer scheme.

However, according to the related art, power transmission environmentbetween a transmission side and a reception side cannot be activelyrecognized upon the wireless power transmission between the transmissionside and the reception side. Thus, a bidirectional communication forsharing state information between the transmission side and thereception side is necessary to achieve more effective and active powertransmission.

SUMMARY OF THE INVENTION

An embodiment provides a wireless power transmitter, a wireless powerreceiver, a wireless power transmission method and a wireless powerreception method, capable of actively and effectively performing powertransmission by transceiving information about the power transmissionstate between the wireless power transmitter and the wireless powerreceiver.

According to one embodiment, there is provided a wireless powertransmission method of a wireless power transmitter for transmittingpower to a wireless power receiver. The wireless power transmissionmethod includes transmitting a connection signal for identifying thewireless power receiver, identifying the wireless power receiver byreceiving a response signal to the connection signal from the wirelesspower receiver, negotiating a power transmission condition with theidentified wireless power receiver and transmitting the power to theidentified wireless power receiver according to the negotiated powertransmission condition.

According to one embodiment, there is provided a wireless powerreception method of a wireless power receiver for receiving power from awireless power transmitter. The wireless power reception method includesreceiving a connection signal for identifying the wireless powerreceiver, transmitting a response signal to the connection signal to thewireless power transmitter, negotiating a power transmission conditionwith the wireless transmitter and receiving the power from the wirelesspower transmitter according to the negotiated power transmissioncondition.

According to one embodiment, there is provided a wireless powertransmitter for transmitting power to a wireless power receiver, thewireless power transmitter including a transmitting unit to transmit aconnection signal for identifying the wireless power receiver, anidentifying unit to identify the wireless power receiver by receiving aresponse signal to the connection signal and a negotiating unit tonegotiate a power transmission condition with the identified wirelesspower receiver, wherein the wireless power transmitter transmits thepower to the identified wireless power receiver according to thenegotiated power transmission condition.

According to one embodiment, there is provided a wireless power receiverfor receiving power from a wireless power transmitter, the wirelesspower receiver including a receiving unit to receive a connection signalfor identifying the wireless power receiver, a transmitting unit totransmit a response signal to the connection signal to the wirelesspower transmitter and a negotiating unit to negotiate a powertransmission condition with the wireless transmitter, wherein thewireless power receiver receives the power from the wireless powertransmitter according to the negotiated power transmission condition.

According to one embodiment, the power transmission can be actively andeffectively achieved by using state information between the wirelesspower transmitter and the wireless power receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a wireless power transmission system accordingto one embodiment;

FIG. 2 is a circuit diagram showing an equivalent circuit of atransmission induction coil according to one embodiment;

FIG. 3 is a circuit diagram showing an equivalent circuit of a powersource and a transmitting unit according to one embodiment;

FIG. 4 is a is a circuit diagram showing an equivalent circuit of areception resonant coil, a reception induction coil, a smoothing circuitand a load according to one embodiment;

FIG. 5 is a block diagram showing a wireless power transmitter and awireless power receiver according to another embodiment;

FIG. 6 is a flowchart showing a wireless power transmission methodaccording to one embodiment;

FIG. 7 is a ladder diagram for explaining a wireless power transmissionmethod according to another embodiment; and

FIG. 8 is a state transition diagram for wireless power transmissionaccording to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a view showing a wireless power transmission system accordingto one embodiment.

Referring to FIG. 1, the wireless power transmission system may includea power supply apparatus 100, a wireless power transmitter 200, awireless power receiver 300, and a load 400.

According to one embodiment, the power supply apparatus 100 may beincluded in the wireless power transmitter 200.

The wireless power transmitter 200 may include a transmission inductioncoil 210 and a transmission resonant coil 220.

The wireless power receiver 300 may include a reception resonant coil310, a reception induction coil 320 and a rectifying unit 330.

Both terminals of the power supply apparatus 100 are connected to bothterminals of the transmission induction coil 210.

The transmission resonant coil 220 may be spaced apart from thetransmission induction coil 210 by a predetermined distance.

The reception resonant coil 310 may be spaced apart from the receptioninduction coil 320 by a predetermined distance.

Both terminals of the reception induction coil 320 are connected to bothterminals of the rectifying unit 330, and the load 400 is connected toboth terminals of the rectifying unit 330. According to one embodiment,the load 400 may be included in the wireless power receiver 300.

The power generated from the power supply apparatus 100 is transmittedto the wireless power transmitter 200. The power received in thewireless power transmitter 200 is transmitted to the wireless powerreceiver 300, that is, has the resonance frequency the same as that ofthe wireless power transmitter 200, through a resonance phenomenon.

Hereinafter, the power transmission process will be described in moredetail.

The power supply apparatus 100 generates AC power having a predeterminedfrequency and transmits the AC power to the wireless power transmitter200.

The transmission induction coil 210 and the transmission resonant coil220 are inductively coupled with each other. In other words, if ACcurrent flows through the transmission induction coil 210 due to thepower received from the power supply apparatus 100, the AC current isinduced to the transmission resonant coil 220 physically spaced apartfrom the transmission induction coil 210 due to the electromagneticinduction.

Thereafter, the power received in the transmission resonant coil 220 istransmitted to the wireless power receiver 300, which makes a resonancecircuit with the wireless power transmitter 200, using resonance.

Power can be transmitted between two LC circuits, which areimpedance-matched with each other, using resonance. The powertransmitted using the resonance can be farther transmitted with higherefficiency when comparing with the power transmitted by theelectromagnetic induction.

The reception resonant coil 310 receives power from the transmissionresonant coil 220 using the resonance. The AC current flows through thereception resonant coil 310 due to the received power. The powerreceived in the reception resonant coil 310 is transmitted to thereception induction coil 320, which is inductively coupled with thereception resonant coil 310, due to the electromagnetic induction. Thepower received in the reception induction coil 320 is rectified by therectifying unit 330 and transmitted to the load 400.

The transmission resonant coil 220 of the wireless power transmitter 200may transmit power to the reception resonant coil 310 of the wirelesspower receiver 300 using a magnetic field. In detail, the transmissionresonant coil 220 and the reception resonant coil 310 areresonance-coupled with each other so that the transmission resonant coil220 and the reception resonant coil 310 operate at a resonancefrequency.

The resonance-coupling between the transmission resonant coil 220 andthe reception resonant coil 310 can significantly improve the powertransmission efficiency between the wireless power transmitter 200 andthe wireless power receiver 300.

A quality factor and a coupling coefficient are important in thewireless power transmission. In other words, the power transmissionefficiency can be gradually improved as the values of the quality factorand the coupling coefficient are increased.

The quality factor may refer to an index of energy that may be stored inthe vicinity of a wireless power transmitter or a wireless powerreceiver.

The quality factor may vary according to the operating frequency w aswell as a shape, a dimension and a material of a coil. The qualityfactor may be expressed as following equation, Q=w*L/R. In the aboveequation, L refers to the inductance of a coil and R refers toresistance corresponding to the quantity of power loss caused in thecoil.

The quality factor may have a value of 0 to infinity. The powertransmission efficiency between the wireless power transmitter 200 andthe wireless power receiver 300 can be improved as the value of thequality factor is increased.

The coupling coefficient represents the degree of inductive magneticcoupling between a transmission coil and a reception coil, and has avalue of 0 to 1.

The coupling coefficient may vary according to the relative position andthe distance between the transmission coil and the reception coil.

FIG. 2 is a circuit diagram showing an equivalent circuit of thetransmission induction coil 210 according to the one embodiment.

As shown in FIG. 2, the transmission induction coil 210 may include aninductor L1 and a capacitor C1, and a circuit having a desirableinductance and a desirable capacitance can be constructed by theinductor L1 and the capacitor C1.

The transmission induction coil 210 may be constructed as an equivalentcircuit in which both terminals of the inductor L1 are connected to bothterminals of the capacitor C1. In other words, the transmissioninduction coil 210 may be constructed as an equivalent circuit in whichthe inductor L1 is connected to the capacitor C1 in parallel.

The capacitor C1 may include a variable capacitor, and impedancematching may be performed by adjusting the capacitance of the capacitorC1. The equivalent circuit of the transmission resonant coil 220, thereception resonant coil 310 and the reception induction coil 320 may bethe same as the equivalent circuit shown in FIG. 2.

FIG. 3 is a circuit diagram showing an equivalent circuit of the powersupply apparatus 100 and the wireless power transmitter 200 according toone embodiment.

As shown in FIG. 3, the transmission induction coil 210 and thetransmission resonant coil 220 may be constructed by using inductors L1and L2 and capacitors C1 and C2 having predetermined inductances andcapacitances, respectively.

FIG. 4 is a circuit diagram showing an equivalent circuit of thewireless power receiver 300 according to one embodiment.

As shown in FIG. 4, the reception resonant coil 310 and the receptioninduction coil 320 may be constructed by using inductors L3 and L4, andcapacitors C3 and C4 having predetermined inductances and capacitances,respectively.

The rectifying unit 330 can transfer DC power to the load 400 byconverting AC power received from the reception induction coil 320 intothe DC power.

In detail, the rectifying unit 330 may include a rectifier and asmoothing circuit. According to one embodiment, the rectifier mayinclude a silicon rectifier and may be equivalent as a diode D1 as shownin FIG. 4.

The rectifier can convert AC power received from the reception inductioncoil 320 into the DC power.

The smoothing circuit can output a smooth DC power by removing ACcomponents included in the DC power converted by the rectifier.According to one embodiment, as shown in FIG. 4, the smoothing circuitmay include a rectifying capacitor C5, but the embodiment is not limitedthereto.

The load 400 may be a predetermined rechargeable battery or a devicerequiring the DC power. For example, the load 400 may refer to abattery.

The wireless power receiver 300 may be installed in an electronicdevice, such as a cellular phone, a laptop computer or a mouse,requiring the power.

The wireless power transmitter 200 may interchange information with thewireless power receiver 300 through in-band communication or anout-of-band communication.

The in-band communication refers to the communication for interchanginginformation between the wireless power transmitter 200 and the wirelesspower receiver 300 through a signal used in the wireless powertransmission. The wireless power receiver 300 may further include aswitch and may receive or may not receive power transmitted from thewireless power transmitter 200 through a switching operation of theswitch. Accordingly, the wireless power transmitter 200 can recognize anon-signal or an off-signal of the switch included in the wireless powerreceiver 300 by detecting the quantity of power consumed in the wirelesspower transmitter 200.

In detail, the wireless power receiver 300 may change the power consumedin the wireless power transmitter 200 by adjusting the quantity of powerabsorbed in a resistor by using the resistor and the switch. Thewireless power transmitter 200 may acquire the state information of thewireless power receiver 300 by detecting the variation of the powerconsumption. The switch may be connected to the resistor in series.According to one embodiment, the state information of the wireless powerreceiver 300 may include information about the present charge amount inthe wireless power receiver 300 and the change of the charge amount.

In more detail, if the switch is open, the power absorbed in theresistor becomes zero, and the power consumed in the wireless powertransmitter 200 is reduced.

If the switch is short-circuited, the power absorbed in the resistorbecomes greater than zero, and the power consumed in the wireless powertransmitter 200 is increased. If the wireless power receiver repeats theabove operation, the wireless power transmitter 200 detects powerconsumed therein to make digital communication with the wireless powerreceiver 300.

The wireless power transmitter 200 receives the state information of thewireless power receiver 300 through the above operation so that thewireless power transmitter 200 can transmit appropriate power.

To the contrary, the wireless power transmitter 200 may include aresistor and a switch to transmit the state information of the wirelesspower transmitter 200 to the wireless power receiver 300.

According to one embodiment, the state information of the wireless powertransmitter 200 may include information about the maximum amount ofpower to be supplied from the wireless power transmitter 200, the numberof wireless power receivers 300 receiving the power from the wirelesspower transmitter 200 and the amount of available power of the wirelesspower transmitter 200.

Hereinafter, the out-of-band communication will be described.

The out-of-band communication refers to the communication performedthrough a specific frequency band other than the resonance frequencyband in order to exchange information necessary for the powertransmission. The wireless power transmitter 200 and the wireless powerreceiver 300 can be equipped with out-of-band communication modules toexchange information necessary for the power transmission. Theout-of-band communication module may be installed in the power supplyapparatus. In one embodiment, the out-of-band communication module mayuse a short-distance communication technology, such as Bluetooth,Zigbee, WLAN or NFC, but the embodiment is not limited thereto.

Hereinafter, a wireless power transmitter, a wireless power receiver, awireless power transmission method, a wireless power reception method,an information transmission method and an information reception methodaccording to another embodiment will be described with reference toFIGS. 5 to 8 as well as FIGS. 1 to 4.

FIG. 5 is a block diagram showing the wireless power transmitter and thewireless power receiver according to another embodiment.

The wireless power transmitter 200 may include a transmitting unit 230,an identifying unit 240, a negotiating unit 250 and a control unit 260.In addition, the wireless power transmitter 200 may further include thetransmission induction coil 210 and the transmission resonant coil 220shown in FIG. 1.

The wireless power receiver 300 may include a receiving unit 350, aresponse signal transmitting unit 360, a negotiating unit 370 and acontrol unit 380. In addition, the wireless power receiver 300 mayfurther include the reception resonant coil 310, the reception inductioncoil 320, the rectifier circuit 330 and the load 400 shown in FIG. 1.

The transmitting unit 230 transmits a connection signal to the receivingunit 350. According to one embodiment, the connection signal refers to apower signal for detecting and identifying the wireless power receiver300. The transmitting unit 230 may periodically transmit the connectionsignal to detect the wireless power receiver 300.

The identifying unit 240 identifies the wireless power receiver 300 byreceiving a response signal to the connection signal. If the identifyingunit 240 does not receive the response signal to the connection signal,the transmission of the connection signal to the corresponding wirelesspower receiver 300 may be stopped. According to one embodiment, theidentifying unit 240 may not receive the response signal when theconnection signal is transmitted to a non-transmittable object, such asa key or a coin, other than a transmittable object.

As the response signal to the connection signal is received in theidentifying unit 240, the negotiating unit 250 may negotiate the powertransmission condition with the identified wireless power receiver 300.According to one embodiment, the power transmission condition may referto the factors required for power transmission or power transmissionstop between the wireless power transmitter 200 and the wireless powerreceiver 300. The power transmission may be achieved or not depending onthe power transmission condition between the wireless power transmitter200 and the wireless power receiver 300.

The control unit 260 controls the wireless power transmitter 200 suchthat the power can be transmitted to the identified wireless powerreceiver 300 according to the negotiated power transmission condition.

The negotiating unit 250 transmits state information of the wirelesspower transmitter 200 to the identified wireless power receiver 300 toallow the identified wireless power receiver 300 to determine specificstate information based on the state information of the wireless powertransmitter 200 and receives the specific state information from theidentified wireless power receiver 300.

According to one embodiment, the state information of the wireless powertransmitter 200 may include information about the maximum amount ofpower to be supplied from the wireless power transmitter 200,information about the number of wireless power receivers 300 receivingthe power from the wireless power transmitter 200 and identificationinformation of the wireless power transmitter 200.

According to one embodiment, the state information of the wireless powerreceiver 300 may include information about the present charge amount inthe wireless power receiver 300 and the change of the charge amount.

The negotiating unit 250 receives the state information of theidentified wireless power receiver 300 to determine specific stateinformation based on the state information of the wireless powerreceiver 300 and the control unit 260 controls the wireless powertransmitter 200 to transmit the power corresponding to the specificstate information to the identified wireless power receiver 300.

According to one embodiment, the negotiating unit 250 transmits theinformation about the available amount of power to the identifiedwireless power receiver 300 to allow the identified wireless powerreceiver 300 to determine the demanded amount of power within the rangeof the available amount of power. After that, if the wireless powerreceiver 300 determines the demanded amount of power, the negotiatingunit 250 receives the information about the demanded amount of power.The control unit 260 transmits power corresponding to the demandedamount of power to the wireless power receiver 300.

Through the above procedure, the power transmission state between thewireless power transmitter 200 and the wireless power receiver 300 canbe detected, so that the active power transmission can be performed.

The wireless power receiver 300 may include the receiving unit 350, theresponse signal transmitting unit 360, the negotiating unit 370 and thecontrol unit 380. In addition, the wireless power receiver 300 mayfurther include the reception resonant coil 310, the reception inductioncoil 320, the rectifier circuit 330 and the load 400 shown in FIG. 1.

The receiving unit 350 may receive the connection signal from thewireless power transmitter 200.

The wireless power receiver 300 can transmit the response signal to thereceived connection signal to the wireless power transmitter 200.

The negotiating unit 370 can negotiate the power transmission conditionwith the wireless power transmitter 200 and the wireless power receiver300 can receive the power from the wireless power transmitter 200 basedon the negotiation result.

According to one embodiment, the negotiating unit 370 receives the stateinformation of the wireless power transmitter 200 to determine specificstate information based on the state information of the wireless powertransmitter 200 and can transmit the determined specific stateinformation to the wireless power transmitter 200. In addition, thewireless power receiver 300 can receive the power corresponding to thespecific state information from the wireless power transmitter 200.

Through the above procedure, the power transmission state between thewireless power transmitter 200 and the wireless power receiver 300 canbe detected, so that the active power transmission can be performed.

FIG. 6 is a flowchart showing a wireless power transmission methodaccording to one embodiment.

Although a wireless power transmission using resonance is describedbelow as an example of the wireless power transmission method accordingto one embodiment, a wireless power transmission using anelectromagnetic induction is also possible.

According to one embodiment, a bidirectional communication can beimplemented through the configuration for changing the amount of currentin the wireless power transmitter 200 and the wireless power receiver300. For instance, the bidirectional communication can be implementedthrough the in-band communication using a variable resistor and a switchor the out-of-band communication. The in-band communication and theout-of-band communication are the same as those described with referenceto FIG. 1.

Referring to FIG. 6, the wireless power transmitter 200 transmits theconnection signal to the wireless power receiver 300 (S101). Accordingto one embodiment, the connection signal refers to a power signal fordetecting and identifying the wireless power receiver 300. The wirelesspower transmitter 200 may periodically transmit the connection signal todetect the wireless power receiver 300.

Upon receiving the connection signal, the wireless power receiver 300transmits the response signal to the wireless power transmitter 200(S103). After that, the wireless power transmitter 200 receives theresponse signal to the connection signal to identify the wireless powerreceiver 300.

If the wireless power transmitter 200 does not receive the responsesignal to the connection signal, the transmission of the connectionsignal to the corresponding wireless power receiver 300 may be stopped.According to one embodiment, the wireless power transmitter 200 may notreceive the response signal when the connection signal is transmitted toa non-transmittable object, such as a key or a coin, other than atransmittable object.

If the wireless power transmitter 200 identifies the wireless powerreceiver 300, the wireless power transmitter 200 negotiates the powertransmission condition with the identified wireless power receiver 300(S105).

If the negotiation between the wireless power transmitter 200 and thewireless power receiver 300 is succeeded (S107), the wireless powertransmitter 200 transmits the power to the wireless power receiver 300based on the negotiated power transmission condition (S109).

Step (S105) of negotiating the power transmission to the identifiedwireless power receiver 300 may include a step of transmitting the stateinformation of the wireless power transmitter 200 to the identifiedwireless power receiver 300 to allow the identified wireless powerreceiver 300 to determine the specific state information based on thestate information of the wireless power transmitter 200 and a step ofreceiving the specific state information from the identified wirelesspower receiver 300.

According to one embodiment, steps 105 to 109 may include the followingprocess. The wireless power transmitter 200 transmits the informationabout the available amount of power to the identified wireless powerreceiver 300 to allow the identified wireless power receiver 300 todetermine the demanded amount of power within the range of the availableamount of power. After that, if the wireless power receiver 300determines the demanded amount of power, the wireless power transmitter200 receives the information about the demanded amount of power. Then,the wireless power transmitter 200 transmits the power corresponding tothe demanded amount of power to the identified wireless power receiver300.

According to one embodiment, steps 105 to 109 may include the followingprocess. As an example, the wireless power transmitter 200 is assumed asit wirelessly transmits the power to a plurality of wireless powerreceivers 300.

Information about the priority of power transmission to the wirelesspower receivers 300 is transmitted from the wireless power transmitter200 to the identified wireless power receiver 300 to allow theidentified wireless power receiver 300 to determine whether it acceptsthe priority determined based on the information about the priority.Then, if the identified wireless power receiver 300 accepts thedetermined priority, the wireless power transmitter 200 transmits thepower based on the priority.

According to one embodiment, steps 105 to 109 may include the followingprocess. As an example, it is assumed that a plurality of wireless powertransmitters 200 are present. Each wireless power transmitter 200transmits the identification information of each wireless powertransmitter 200 to the identified wireless power receiver 300 to allowthe identified wireless power receiver 300 to determine one of thewireless power transmitters 200. Then, if the identified wireless powerreceiver 300 selects a specific wireless power transmitters 200, theselected wireless power transmitters 200 receives a selection requestsignal from the identified wireless power receiver 300 and transmits thepower to the identified wireless power receiver 300.

According to one embodiment, in the negotiation step, the wireless powertransmitter 200 requests the state information of the wireless powerreceiver 300 and the state information of the wireless power receiver300 is transmitted to the wireless power transmitter 200 in response tothe request. In contrast, in the negotiation step, the wireless powerreceiver 300 may request the state information of the wireless powertransmitter 200 and the state information of the wireless powertransmitter 200 may be transmitted to the wireless power receiver 300 inresponse to the request.

According to one embodiment, in the negotiation step, the powertransmission is determined based on the state information of thewireless power transmitter 200 and the wireless power receiver 300.

According to one embodiment, the state information of the wireless powertransmitter 200 may refer to information about the number of thewireless power receivers 300 that receive the power from one wirelesspower transmitter 200.

According to one embodiment, if the identification number is given foreach wireless power receiver 300, the state information of the wirelesspower transmitter 200 may refer to information about the givenidentification numbers of the wireless power receivers 300 that receivethe power from a specific wireless power transmitter 200.

According to one embodiment, the state information of the wireless powertransmitter 200 may refer to information about the amount of powersupplied to the wireless power receiver 300.

According to one embodiment, when the power is transmitted to aplurality of wireless power receivers 300, the state information of thewireless power transmitter 200 may refer to information about thepriority of power transmission to the wireless power receivers 300.

According to one embodiment, when the power is transmitted to aplurality of wireless power receivers 300, the state information of thewireless power transmitter 200 may refer to information about thedifferential ratio of the power transmission to the wireless powerreceivers 300. For instance, when a specific wireless power transmitter200 transmits the power to three wireless power receivers 300, thespecific wireless power transmitter 200 may transmit the power to thethree wireless power receivers 300 at the differential ratio of 50%, 30%and 20%, respectively.

According to one embodiment, the state information of the wireless powerreceiver 300 may refer to information about the present charge amount orthe change of the charge amount in the wireless power receiver 300.

According to one embodiment, the state information of the wireless powerreceiver 300 may refer to information about the wireless powertransmitter 200 that transmits the power to the wireless power receiver300. That is, the state information of the wireless power receiver 300may signify the identification information of the wireless powerreceiver 300 that receives the power.

If the negotiation between the wireless power transmitter 200 and thewireless power receiver 300 is succeeded (S107), the wireless powertransmitter 200 transmits the power to the identified wireless powerreceiver 300 based on the negotiated power transmission condition(S109).

If the state of the wireless power transmitter 200 is changed during thepower transmission process (S111), the process returns to negotiationstep S105 or the power transmission is stopped.

According to one embodiment, the change of the state of the wirelesspower transmitter 200 may refer to information about the change of theamount of power to be supplied from the wireless power transmitter 200.In this case, if the amount of power to be supplied from the wirelesspower transmitter 200 is reduced due to the external factors, thewireless power transmitter 200 stops the power transmission and theprocess enters negotiation step S105 to perform the negotiation foradjusting the amount of power transmission between the wireless powertransmitter 200 and the wireless power receiver 300. Then, if thenegotiation for adjusting the amount of power transmission is succeeded,the power transmission is performed. Otherwise, the process again entersnegotiation step S105. If the power supplied to the wireless powertransmitter 200 is shut off or the wireless power receiver 300 has beencharged, the power transmission is finished.

According to one embodiment, the change of the state of the wirelesspower transmitter 200 may refer to information about the change of thenumber of wireless power receivers 300 receiving the power from thewireless power transmitter 200.

If the state of the wireless power receiver 300 is changed during thepower transmission process (S113), the process returns to negotiationstep S105 or the power transmission is stopped.

According to one embodiment, the change of the state of the wirelesspower receiver 300 may signify the detection of a new wireless powerreceiver 300 besides the wireless power receiver 300 that receives thepower from the wireless power transmitter 200.

FIG. 7 is a ladder diagram for explaining a wireless power transmissionmethod according to another embodiment.

Referring to FIG. 7, the wireless power transmitter 200 requests thestate information to each of wireless power transmitters 201, 202 and203 (S201). Although only three wireless power transmitters 201, 202 and203 are illustrated in FIG. 7, the embodiment is not limited thereto. Inaddition, each of the wireless power transmitters 201, 202 and 203 mayinclude the configuration of the wireless power transmitter 200described with reference to FIG. 5. The state information of thewireless power transmitter 200 may include information about the maximumamount of power to be supplied from the wireless power transmitter 200,the number of wireless power receivers 300 receiving the power from thewireless power transmitter 200 and the amount of available power of thewireless power transmitter 200, but the embodiment is not limitedthereto.

According to one embodiment, the wireless power transmitter 200 maytransceive information to/from other wireless power transmitters 201,202 and 203 through the in-band communication or the out-of-bandcommunication.

Then, the wireless power transmitter 200 receives the state informationof the wireless power transmitters 201, 202 and 203, respectively, inresponse to the request for the state information (S203).

In addition, the wireless power transmitter 200 creates the state listbased on the received state information of the wireless powertransmitters 201, 202 and 203 (S205). According to one embodiment, thestate list may be created by collecting the state information of thewireless power transmitters 201, 202 and 203. The state list will bedescribed in more detail with reference to table 1.

TABLE 1 State information of wireless power transmitter Wireless powerMaximum Number of Available transmitter amount of power wireless amount(ID symbol) to be supplied power receivers of power Wireless power 100 W4 20 W transmitter A Wireless power 200 W 5 15 W transmitter B Wirelesspower 300 W 6 30 W transmitter C

Table 1 is an example of the state list created by the wireless powertransmitter 200 based on the state information received from threewireless power transmitters A, B and C. In addition, although not shownin the drawing, the wireless power transmitter 200 may create the statelist by adding the state information of the wireless power transmitter200 to the state list.

Referring to table 1, the maximum amount of power to be supplied fromthe wireless power transmitter A is 100 W, and the wireless powertransmitter A supplies the power to four wireless power receivers 300.In addition, the available amount of power in the wireless powertransmitter A is 20 W. The available amount of power refers to theamount of power to be supplied to another wireless power receiver 300except for the four wireless power receivers 300. In addition, thedemanded amount of power of the four wireless power receivers 300 maynot be needed to be constant, but may vary.

The available amount of power in the wireless power transmitter may varydepending on the wireless power transmitters 201, 202 and 203.

The maximum amount of power of the wireless power transmitter B is 200 Wand the wireless power transmitter B supplies the power to five wirelesspower receivers 300. In addition, the available amount of power in thewireless power transmitter B is 15 W. Further, the demanded amount ofpower of the five wireless power receivers 300 may not be needed to beconstant, but may vary.

The maximum amount of power of the wireless power transmitter C is 300 Wand the wireless power transmitter C supplies the power to six wirelesspower receivers 300. In addition, the available amount of power in thewireless power transmitter C is 30 W. Further, the demanded amount ofpower of the six wireless power receivers 300 may not be needed to beconstant, but may vary.

After that, the wireless power transmitter 200 receives the request fortransmission of the state list from the wireless power receiver 300(S207). According to one embodiment, the wireless power transmitter 200and the wireless power receiver 300 may transceive information throughthe in-band communication or the out-of-band communication.

Then, the wireless power transmitter 200 transmits the state list to thewireless power receiver 300 in response to the request for thetransmission of the state list (S209).

Thereafter, the wireless power receiver 300 selects at least one of thewireless power transmitters 201, 202 and 203 based on the received statelist to receive the power (S211). That is, the wireless power receiver300 may select at least one of the wireless power transmitters 201, 202and 203 based on the state information of each wireless powertransmitter, that is, the maximum of the power to be supplied, thenumber of the wireless power receivers that receive the power from eachwireless power transmitter and the available amount of power in eachwireless power transmitter.

According to one embodiment, the wireless power receiver 300 may selectthe wireless power transmitter 203 having the highest available amountof power from among the wireless power transmitters 201, 202 and 203.Such a selection signifies that the wireless power receiver 300 requiresthe power of 25 W so the wireless power receiver 300 selects thewireless power transmitter capable of supplying the power of 25 W.However, the embodiment is not limited to the above and the wirelesspower receiver 300 may select two wireless power transmitters 201 and203.

According to one embodiment, the wireless power receiver 300 may selectthe wireless power transmitter A, which transmits the power to thewireless power receivers 300 of the fewest number, from among thewireless power transmitters 201, 202 and 203.

In this manner, the wireless power receiver 300 can select the wirelesspower transmitter suitable for the power transmission based on the statelist.

After that, the wireless power receiver 300 transmits information aboutthe selection of at least one wireless power transmitter to the wirelesspower transmitter 200 (S213). The selection information may includeinformation about the wireless power transmitter selected by thewireless power receiver 300 from among the wireless power transmitters201, 202 and 203. In detail, if the wireless power transmitters 201, 202and 203 have identification symbols A, B and C, respectively, theselection information may include information about the identificationsymbols.

The wireless power transmitter 200 requests the power transmission tothe wireless power transmitter 201 selected based on the receivedselection information (S215). In FIG. 7, the wireless power transmitter200 requests the power transmission to the wireless power transmitter201, but the embodiment is not limited thereto.

The selected wireless power transmitter 201 transmits the power to thewireless power receiver 300 (S217). According to one embodiment, theselected wireless power transmitter 201 may wirelessly transmit thepower to the wireless power receiver 300 using electromagnetic inductionor resonance.

In this manner, according to the embodiment, the wireless powertransmitter 200 and the wireless power receiver 300 may share theinformation through the bidirectional communication, so that the activepower transmission can be achieved based on the power condition. Thus,the power transmission can be effectively performed between the wirelesspower transmitter 200 and the wireless power receiver 300.

FIG. 8 is a state transition diagram for wireless power transmissionaccording to one embodiment.

Hereinafter, the state transition diagram for the wireless powertransmission according to one embodiment will be described withreference to FIGS. 1 to 7.

First Mode (Selection Mode)

At first, the wireless power transmission system including the wirelesspower transmitter 200 and the wireless power receiver 300 is in a firstmode M1. According to one embodiment, the first mode M1 may be theselection mode. In the first mode, the wireless power transmitter 200may manage an interface region for removal and arrangement of objects.

If the wireless power transmitter 200 detects at least one object, thewireless power transmitter 200 must try to detect the position of the atleast one object. In particular, the wireless power transmitter 200 maytry to distinguish the wireless power receiver 300 capable of receivingthe power from other foreign objects (for instance, key or coin).

In addition, the wireless power transmitter 200 must try to select thewireless power receiver 300 for power transmission. If the wirelesspower transmitter 200 has no sufficient information for accomplishingthe above purposes at the early stage, the wireless power transmitter200 sequentially and repeatedly performs the connection mode and theidentification and setting mode, which will be described later, and thenperforms the selection mode.

Second Mode (Connection Mode)

According to one embodiment, the second mode M2 may be the connectionmode. In the second mode M2, the wireless power transmitter 200 may havebeen ready to make communication with the wireless power receiver 300.

If the wireless power transmitter 200 detects the wireless powerreceiver 300 in the first mode M1, the wireless power transmissionsystem is transited to the second mode M2 to transmit the power to thewireless power receiver 300. That is, if the existence of the wirelesspower receiver 300 is recognized, the wireless power transmission systemis transited to the second mode M2 to transmit the connection signal tothe wireless power receiver 300. The connection signal is transmittedfrom the wireless power transmitter 200 to the wireless power receiver300 to receive the state information of the wireless power receiver 300.

If the wireless power transmitter 200 does not receive the responsesignal to the connection signal from the wireless power receiver 300,the transmission of the connection signal is stopped and the wirelesspower transmission system is transited to the first mode M1. If thewireless power transmitter 200 receives the response signal, whichrepresents that the load (or battery) 400 has been sufficiently charged,from the wireless power receiver 300, the wireless power transmitter 200finishes the power transmission.

If the wireless power transmitter 200 receives the response signalrequesting the power transmission from the wireless power receiver 300in the second mode M2, the wireless power transmitter 200 may transmitan additional connection signal to a new wireless power receiver 300.The additional connection signal signifies a signal for detecting thenew wireless power receiver 300.

If there is no response signal to the additional connection signal ofthe wireless power transmitter 200, the operation for detecting the newwireless power receiver 300 is stopped.

Third Mode (Identification and Setting Mode)

If the wireless power transmitter 200 has received the response signalto the connection signal from the wireless power receiver 300 in thesecond mode M2, the wireless power transmission system is transited tothe third mode M3 for collecting identification information and stateinformation of the wireless power receiver 300. According to oneembodiment, the third mode M3 may be the identification and settingmode. The identification information of the wireless power receiver 300may refer to the sort, type or model of the wireless power receiver 300,but the embodiment is not limited thereto. The state information of thewireless power receiver 300 may signify the maximum amount of power (ormaximum amount of charge) to be supplied to the load (or battery) 400and the present amount of power remaining in the load (or battery) 400,but the embodiment is not limited thereto. The wireless powertransmitter 200 uses the identification information and stateinformation of the wireless power receiver 300 to establish the powertransmission condition with respect to the wireless power receiver 300.The power transmission condition may refer to the group of conditionsfor specifying the power transmission from the wireless powertransmitter 200 to the wireless power receiver 300.

If there is restriction for the power transmission condition in thethird mode M3, the wireless power transmission system is transited tothe first mode M1. According to one embodiment, the restriction for thepower transmission condition may refer to the non-establishment of thepower transmission condition. According to one embodiment, therestriction for the power transmission condition may signify a case inwhich an unexpected data packet is transmitted between the wirelesspower transmitter 200 and the wireless power receiver 300. According toone embodiment, the restriction for the power transmission condition mayrefer to a situation, such as a time out. The time out may include acase in which the power transmission is stopped after a predeterminedtime has elapsed from the removal of the wireless power receiver 300that receives the power.

If the wireless power transmission system is transited to the first modeM1 due to the restriction for the power transmission condition in thethird mode M3, the wireless power transmitter 200 transmits the stateinformation related to the wireless power transmitter 200 to thewireless power receiver 300 and then the wireless power transmissionsystem is transited again to the third mode M3. According to oneembodiment, the state information of the wireless power transmitter 200may refer to information about the number of wireless power receivers300 that receive the power from one wireless power transmitter 200.

According to one embodiment, if the identification number is dedicatedfor each wireless power receiver 300, the state information of thewireless power transmitter 200 may refer to information about thededicated identification numbers of the wireless power receivers 300that receive the power from a specific wireless power transmitter 200.

According to one embodiment, the state information of the wireless powertransmitter 200 may refer to information about the amount of powersupplied to the wireless power receiver 300.

According to one embodiment, when the power is transmitted to aplurality of wireless power receivers 300, the state information of thewireless power transmitter 200 may refer to information about thepriority of power transmission to the wireless power receivers 300.

According to one embodiment, when the power is transmitted to aplurality of wireless power receivers 300, the state information of thewireless power transmitter 200 may refer to information about thedifferential ratio of the power transmission to the wireless powerreceivers 300. For instance, when a specific wireless power transmitter200 transmits the power to three wireless power receivers 300, thespecific wireless power transmitter 200 may transmit the power to thethree wireless power receivers 300 at the differential ratio of 50%, 30%and 20%, respectively.

In the number of the wireless power receivers 300 exceeds a certainnumber in the third mode M3, the wireless power transmission system istransited again to the first mode M1. That is, when the specificwireless power transmitter 200 supplies the power to five wireless powerreceivers 300, if a new wireless power receiver 300 is detected, thewireless power transmission system is transited to the first mode M1such that the power cannot be transmitted to the new wireless powerreceiver 300.

Fourth Mode (Power Transmission)

If the power transmission condition is established in the third mode M3,the wireless power transmission system may be transited to the fourthmode M4. According to one embodiment, the fourth mode M4 refers to thestate in which the wireless power transmitter 200 supplies the power tothe wireless power receiver 300. According to one embodiment, the fourthmode M4 refers to the state in which the wireless power transmitter 200supplies the power to the wireless power receiver 300 while adjustingthe current flowing through a coil in response to information receivedfrom the wireless power receiver 300.

If one of the power transmission conditions is not established in thefourth mode M4, the power transmission from the wireless powertransmitter 200 to the wireless power receiver 300 is stopped and thewireless power transmission system is transited to the first mode M1.According to one embodiment, the restriction for the power transmissioncondition may refer to the non-establishment of the power transmissioncondition. According to one embodiment, the restriction for the powertransmission condition may signify a case in which an unexpected datapacket is transmitted between the wireless power transmitter 200 and thewireless power receiver 300. According to one embodiment, therestriction for the power transmission condition may refer to asituation, such as a time out. The time out may include a case in whichthe power transmission is stopped after a predetermined time has elapsedfrom the removal of the wireless power receiver 300 that receives thepower.

If the wireless power transmitter 200 receives the response signal,which represents that the load (or battery) 400 has been sufficientlycharged, from the wireless power receiver 300 in the fourth mode M4, thewireless power transmitter 200 finishes the power transmission and thewireless power transmission system is transited to the first mode M1.

If the state of the wireless power receiver 300 is changed in the fourthmode M4, the wireless power transmission system may be transited to thethird mode M3.

According to one embodiment, the change of the state of the wirelesspower receiver 300 may signify the detection of a new wireless powerreceiver 300 during the power transmission from the wireless powertransmitter 200 to the wireless power receiver 300. In this case, thewireless power transmission system is transited from the fourth mode M4to the third mode M3. After that, the wireless power transmitter 200works to collect the identification information and state information ofthe wireless power receiver 300 and the wireless power transmissionsystem is transited to the fourth mode M4 if the wireless powertransmission condition has been established. In addition, the wirelesspower transmission system is transited to the first mode M1 if there isrestriction for the wireless power transmission condition.

According to one embodiment, the change of the state of the wirelesspower receiver 300 may refer to the detection of at least one newwireless power receiver 300 due to the excessive number of the wirelesspower receivers 300 that receive the power from the wireless powertransmitter 200. In this case, the wireless power transmission system istransited from the fourth mode M4 to the third mode M3. Then, thewireless power transmitter 200 works to collect the identificationinformation and state information of the wireless power receiver 300 andthe wireless power transmission system is transited to the first mode M1with respect to the excessive wireless power receivers 300.

Fifth Mode (Power Transmission and Bidirectional Communication)

The wireless power transmission system may be transited from the fourthmode M4 to the fifth mode M5 to allow the wireless power transmitter 200and the wireless power receiver 300 to share information.

According to one embodiment, the fifth mode M5 may be a powertransmission and bidirectional communication mode. According to oneembodiment, the power transmission is performed between the wirelesspower transmitter 200 and the wireless power receiver 300 and thewireless power transmitter 200 and the wireless power receiver 300 mayshare the information about the change of the state thereof in the fifthmode M5.

According to one embodiment, the information about the change of thestate of the wireless power transmitter 200 may refer to informationabout the change of the number of wireless power transmitters 200 andthe change of the amount of power to be supplied from the wireless powertransmitter 200.

According to one embodiment, the information about the change of thestate of the wireless power transmitter 200 may refer to informationabout the change of the number of wireless power receivers 300 thatreceive the power from one wireless power transmitter 200.

According to one embodiment, if the identification number is dedicatedfor each wireless power receiver 300, the information about the changeof the state of the wireless power transmitter 200 may refer toinformation about the dedicated identification numbers of the wirelesspower receivers 300 that receive the power from a specific wirelesspower transmitter 200.

According to one embodiment, the information about the change of thestate of the wireless power transmitter 200 may refer to informationabout the amount of power supplied to the wireless power receiver 300.

According to one embodiment, when the power is transmitted to aplurality of wireless power receivers 300, the information about thechange of the state of the wireless power transmitter 200 may refer toinformation about the priority of power transmission to the wirelesspower receivers 300.

According to one embodiment, when the power is transmitted to aplurality of wireless power receivers 300, the information about thechange of the state of the wireless power transmitter 200 may refer toinformation about the differential ratio of the power transmission tothe wireless power receivers 300. For instance, when a specific wirelesspower transmitter 200 transmits the power to three wireless powerreceivers 300, the specific wireless power transmitter 200 may transmitthe power to the three wireless power receivers 300 at the differentialratio of 50%, 30% and 20%, respectively.

If there is restriction for the power transmission condition in thefifth mode M5, the wireless power transmission system is transited tothe first mode M1. According to one embodiment, the restriction for thepower transmission condition may refer to the non-establishment of thepower transmission condition. According to one embodiment, therestriction for the power transmission condition may signify a case inwhich an unexpected data packet is transmitted between the wirelesspower transmitter 200 and the wireless power receiver 300. According toone embodiment, the restriction for the power transmission condition mayrefer to a situation, such as a time out. The time out may include acase in which the power transmission is stopped after a predeterminedtime has elapsed from the removal of the wireless power receiver 300that receives the power.

If the wireless power transmission system is transited to the first modeM1 due to the restriction for the power transmission condition in thefifth mode M5, the wireless power transmitter 200 transmits the stateinformation related to the wireless power receivers 300 to the wirelesspower receiver 300 and then the wireless power transmission system istransited again to the fifth mode M3.

If the wireless power transmitter 200 receives the response signal,which represents that the load (or battery) 400 has been sufficientlycharged, from the wireless power receiver 300 in the fifth mode M5, thewireless power transmitter 200 finishes the power transmission and thewireless power transmissions system is transited to the first mode M1.

If the state of the wireless power receiver 300 is changed in the fifthmode M5, the wireless power transmission system may be transited to thefourth mode M4.

According to one embodiment, the change of the state of the wirelesspower receiver 300 may signify the detection of a new wireless powerreceiver 300 during the power transmission from the wireless powertransmitter 200 to the wireless power receiver 300 through thebidirectional communication.

In this case, the wireless power transmission system is transited fromthe fifth mode M5 to the fourth mode M4. After that, the wireless powertransmitter 200 works to collect the identification information andstate information of a new wireless power receiver 300 and the wirelesspower transmission system is transited again to the fifth mode M4 if thewireless power transmission condition has been established. In addition,the wireless power transmission system is transited to the first mode M1if there is restriction for the wireless power transmission condition.

Although the embodiment has been described with reference to thewireless power transmission using the resonance, the wireless powertransmission method, the wireless power reception method and the powercontrol method using the bidirectional communication according to theembodiment may be applicable for other wireless power transmissionsusing the electromagnetic induction or the RF scheme.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A method for transmitting wireless power by awireless power transmitter, the method comprising: performing aninitiation process with a wireless power receiver, the initiationprocess comprising: transmitting a connection signal to the wirelesspower receiver for detecting and identifying the wireless powerreceiver, and in response to transmitting the connection signal,receiving a response signal from the wireless power receiver andidentifying the wireless power receiver based on the response signal;performing a negotiation process with the wireless power receiver fornegotiating a power transmission condition, the negotiation processbeing performed in a specific order comprising: receiving a requestsignal from the wireless power receiver to retrieve a capability of thewireless power transmitter, the capability including a first availableamount of power of the wireless power transmitter, transmitting thecapability to the wireless power receiver, in response to the requestsignal, so that the wireless power receiver determines a demanded amountof power based on the first available amount of power, and receiving thedemanded amount of power to set up the power transmission condition fromthe wireless power receiver, the demanded amount of power being lessthan the first available amount of power of the wireless powertransmitter; transmitting first wireless power to the wireless powerreceiver based on the power transmission condition when the demandedamount of power is less than the first available amount of power andallowable by the wireless power transmitter based on the capability ofthe wireless power transmitter; in response to a state of the wirelesspower transmitter changing to a reduced capability based on an externalfactor while conducting power transmission, stopping transmission of thefirst wireless power and directly re-entering the negotiation processwith the wireless power receiver without re-entering the initiationprocess to generate an adjusted power transmission condition differentthan the power transmission condition; and after the re-entering of thenegotiation process, transmitting second wireless power to the wirelesspower receiver without re-entering the initiation process according tothe adjusted power transmission condition, the second wireless powerbeing different than the first wireless power.
 2. The method of claim 1,further comprising: in response to a state of the wireless powerreceiver changing while conducting power transmission, re-entering thenegotiation process with the wireless power receiver to adjust the powertransmission condition.
 3. The method of claim 1, wherein the demandedamount of power of the wireless power receiver is within a range of thefirst available amount of power of the wireless power transmitter.
 4. Amethod for receiving wireless power by a wireless power receiver, themethod comprising: performing an initiation process with a wirelesspower transmitter, the initiation process comprising: receiving aconnection signal from the wireless power transmitter for detecting andidentifying the wireless power receiver, and in response to receivingthe connection signal, transmitting a response signal to the wirelesspower transmitter including information for identification of thewireless power receiver; performing a negotiation process with thewireless power transmitter for negotiating a power transmissioncondition, the negotiation process being performing in a specific ordercomprising: transmitting a request signal to the wireless powertransmitter to retrieve a capability of the wireless power transmitter,receiving the capability from the wireless power transmitter in responseto the request signal, the capability including a first available amountof power of the wireless power transmitter, determining a demandedamount of power that is less than the first available amount of power,and transmitting the demanded amount of power to set up the powertransmission condition to the wireless power transmitter; receivingfirst wireless power from the wireless power transmitter based on thepower transmission condition when the demanded amount of power is lessthan the first available amount of power and allowable by the wirelesspower transmitter based on the capability of the wireless powertransmitter; in response to a state of the wireless power transmitterchanging to a reduced capability based on an external factor duringpower transmission, losing reception of the first wireless power anddirectly re-entering the negotiation process with the wireless powertransmitter without re-entering the initiation process to generate anadjusted power transmission condition different than the powertransmission condition; and after the re-entering of the negotiationprocess, receiving second wireless power from the wireless powertransmitter without re-entering the initiation process according to theadjusted power transmission condition, the second wireless power beingdifferent than the first wireless power.
 5. The method of claim 4,further comprising: in response to a state of the wireless powerreceiver changing while conducting power transmission, re-entering thenegotiation process with the wireless power transmitter to adjust thepower transmission condition.
 6. The method of claim 4, wherein thedemanded amount of power of the wireless power receiver is within arange of the first available amount of power of the wireless powertransmitter.
 7. A wireless power receiver for receiving wireless power,the wireless power receiver comprising a controller configured to:perform an initiation process with a wireless power transmitter, theinitiation process comprising: receiving a connection signal from thewireless power transmitter for detecting and identifying the wirelesspower receiver, and in response to receiving the connection signal,transmitting a response signal to the wireless power transmitterincluding information for identification of the wireless power receiver;perform a negotiation process with the wireless power transmitter fornegotiating a power transmission condition, the negotiation processbeing performed in a specific order comprising: transmitting a requestsignal to the wireless power transmitter to retrieve a capability of thewireless power transmitter, receiving the capability from the wirelesspower transmitter in response to the request signal, the capabilityincluding a first available amount of power of the wireless powertransmitter, determining a demanded amount of power that is less thanthe first available amount of power, and transmitting the demandedamount of power to set up the power transmission condition to thewireless power transmitter; a coil configured to receive first wirelesspower from the wireless power transmitter based on the powertransmission condition when the demanded amount of power is less thanthe first available amount of power and allowable by the wireless powertransmitter based on the capability of the wireless power transmitter;and a rectifier configured to transfer DC power to a load by convertingthe wireless power received from the wireless power transmitter, whereinthe controller is further configured to: in response to a state of thewireless power transmitter changing to a reduced capability based on anexternal factor during power transmission, directly re-enter thenegotiation process with the wireless power transmitter withoutre-entering the initiation process to generate an adjusted powertransmission condition different than the power transmission condition,and wherein the coil is further configured to after the re-entering ofthe negotiation process, receive second wireless power from the wirelesspower transmitter without re-entering the initiation process accordingto the adjusted power transmission condition, the second wireless powerbeing different than the first wireless power.
 8. The wireless powerreceiver of claim 7, wherein the controller is further configured to: inresponse to a state of the wireless power receiver changing whileconducting power transmission, re-enter the negotiation process with thewireless power transmitter to adjust the power transmission condition.9. The wireless power receiver of claim 7, wherein the demanded amountof power of the wireless power receiver is within a range of the firstavailable amount of power of the wireless power transmitter.